1. Field of the Invention
This invention relates to air assist devices of fuel injection type internal combustion engines, and more particularly to improvements in an air assist device of a fuel injection type internal combustion engine, suitable for use in a motor vehicle engine having an electronically controlled fuel injection device, and having an air assisted injector provided close to a nozzle thereof with an adapter constituting an assist air introducing portion, whereby assist air introduced into the assist air introducing portion through assist air intake ports formed in the peripheral wall of the adapter is blown out of an assist air jet formed at the bottom of the adapter together with fuel, so that atomization of fuel can be facilitated.
2. Description of the Prior Art
An electronically controlled fuel injection device has been used in one of systems for controlling the air-fuel ratio of gasified fuel-air mixture in internal combustion engines such as engines used for motor vehicles. The internal combustion engine having the electronically controlled fuel injection device of the type described is of such an arrangement that, for example, a fuel injection time is determined commensurate to an intake air flowrate of the engine, an engine rotational speed and the like, and an air-fuel ratio of the engine is controlled by opening an injector provided on an intake manifold, for example, for flowing out fuel into an air intake port of the engine only for the aforesaid fuel injection time. The electronically controlled fuel injection devices of the type described have been widely used for the engines of motor vehicles, to which is adopted exhaust gas purification measure, requiring precise control of the air-fuel ratio.
Recently, there has been tried to feed part of intake air to a position close to a nozzle of an injector so as to facilitate the atomization of fuel blown out of the injector under the air flow velocity, thus achieving an effect to a certain extent. As shown in FIGS. 1 and 2, the air assist device of the type described comprises: an air assisted injector 14 provided close to a nozzle 14a thereof with an adapter 16 for the air assist, constituting an assist air introducing portion 18; a fuel delivery pipe 20 for supplying fuel to the air assisted injector 14; an assist air path 22 formed in the intake manifold 12 for supplying assist air to the assist air introducing portion 18; a ring shaped abutting rubber seal 24 additionally functioning as a heat insulator for shutting the periphery of the adapter 16 off the interior of the intake manifold 12; and also a ring-shaped abutting rubber seal 26 for shutting the periphery of the adapter 16 off the atmosphere, whereby, for example, assist air introduced through a small number of elliptical assist air intake ports 16a into the assist air introducing portion 18 is blown out of an assist air jet 16b formed at the bottom of the adapter 16 together with fuel, so that the atomization of fuel can be facilitated. In the drawings, designated at 28 is an assist air pipe line, 30 a flange, 32 a bolt, 12a a mounting hole for the air assisted injector 14, 14b a pintle of the air assisted injector 14, and 14c a housing of the air assisted injector 14.
The air assist device of the type described makes it possible to facilitate the atomization of fuel blown out of the nozzle of the air assisted injector 14, and heretofore, in order to minimize the loss in pressure in the assist air path, the diameter of each opening of the assist air intake ports 16a has been made as large as allowable in design, or each opening has been formed into an elliptical shape or the like. However, in order to maximize the air assist effect, a diameter A of an opening of an assist air jet 16b is contracted. In consequence, if extraneous matters, which have made ingress into the assist air path 22 from some cause or other, enter the adapter 16 through the assist air intake ports 16a and block the assist air jet 16b, whereby fuel cannot satisfactorily be supplied to the relevant cylinder, thus possibly causing a misfire. Additionally, when the assist air intake ports 16a are formed into elliptical shapes, unbalanced portions have been formed in the flow of assist air, thereby possibly resulting in unsatisfactory atomizing of fuel.
Furthermore, heretofore, there have been cases where satisfactory atomization of fuel should not necessarily be made depending upon the direction of introducing assist air into the adapter 16. To obviate the above-described disadvantages, there has been proposed an air assist device, in which there is provided a swirl injector for rendering swirls to injected fuel. Or, there has been proposed an air assist device, in which there is provided at the forward end of the air assisted injector 14 inclosely attached state a cap-shaped adapter 16 formed along an inner wall thereof with assist air introducing grooves 18a for communicating the assist air intake ports 16a and the assist air jet 16b with each other as shown in FIGS. 3 and 4, and the aforesaid assist air introducing grooves are disposed in directions tangential to the assist air jet 16b so as to further render swirls to the flow of assist air. The former is advantageous in the case of a constant flow which is produced by a one-point injection obtained by the provision of an injector in a throttle body, however, not advantageous in the case of a multiple point injection in which injectors are provided on respective cylinders and opened for a short period of time. The latter is complicated in construction, and moreover, has assist air introducing portions constituted by narrow grooves, whereby an assist air flowrate becomes insufficient due to the loss in pressure, thus unabling to achieve the practical results.